1. Field of the Invention
This invention relates to a playback apparatus which can be used for playing back at least two-types of frequency-modulated signals recorded on a recording medium by different recording systems. More particularly, the invention relates to a playback apparatus for still-video signals recorded on a magnetic floppy disk.
2. Description of the Prior Art
Recording systems for recording still-video signals on a high-density magnetic floppy disk by an electronic still camera (still-video camera) or other recording apparatuses, are of two types, namely a normal-band recording system and a high-band recording system.
A still-video signal comprises a luminance signal (Y signal) and a color signal (C signal) (in general, color difference signals R-Y and B-Y). In the normal-band mode, a carrier wave having a center frequency of 7 MHz is frequency modulated by the luminance signal Y (this frequency-modulated wave is called a "Y-RF signal" for short), carrier waves having frequencies of 1.2 MHz and 1.3 MHz are frequency modulated by the color difference signals R-Y, B-Y, respectively (these frequency-modulated waves are called "C-RF signals" for short), and the Y-RF, C-RF signals are mixed and recorded on the track of a video floppy. The frequency of the sync tip of the Y-RF signal is 6 MHz, the frequency of the white peak is 7.5 MHz, and the frequency deviation is 1.5 MHz.
In the high-band recording system for recording high-resolution still-video signals, the center frequency of the carrier wave for frequency modulation of the luminance signal Y is set at 9 MHz. The sync tip frequency of the Y-RF signal in the high-band recording frequency is 7.7 MHz, the white peak frequency is 9.7 MHz, and the frequency deviation is 2 MHz. The C-RF signal is the same as in the case of the normal band.
When the recording system of a still-video signal differs from another, the playback system also differs, particularly the construction of the frequency demodulator circuit and its peripheral circuitry. Accordingly, in a playback apparatus usable for both the normal band and high band, two Y-RF signal demodulator circuits are provided, one for the normal-band system and one for the high-band system. Also, with regard to low-pass filters connected in back of these demodulator circuits in order to remove the carrier wave components, filters having different cut-off frequencies will be required since the frequencies of the carrier-wave signals will not be the same for both the normal-band recording system and high-band recording system.
However, since filters having different cut-off frequencies possess different amounts of delay, the amounts by which the signals passing through the filters are delayed will not be the same for both the normal-band recording system and high-band recording system.
The C-RF signal likewise is demodulated by using demodulator circuits and low-pass filter circuits, and these circuits also possess their own signal delays. Since it is required that the luminance signal and color signal be in synchronism after demodulation, the conventional practice is to provide a delay circuit in conformity with the difference in the amounts of delay of the luminance and color signals. However, since the amount of delay of the luminance signal differs depending upon the recording system, synchronization measures in conformance with the recording system are also required.
Further, the color signal is formed by line-sequencing the color difference signals R-Y and B-Y. This means that color signal playback requires a synchronizing circuit, and the playback apparatus is provided with a circuit for this purpose. Moreover, the playback apparatus is provided with a comb filter for improving the color represented by the outputted color difference signal. However, the synchronizing circuit and comb filter possess characteristics that delay the signal passing through the respective circuit elements, so that the color signal which has passed through the circuit elements is delayed in comparison with the luminance signal in 1 H of time (where H is one horizonal scanning interval). Consequently, these circumstances must be taken into consideration for the sake of color signal and luminance signal synchronization.